In the related art, a multilayer printed circuit board has been manufactured by impregnating a glass cloth base material with an epoxy resin, semi-curing the resin to prepare a prepreg sheet, placing one or more of the prepreg sheets on a circuit board with a circuit, further placing a copper foil on the sheet, and integrally molding the product under pressure using a hot-plate press. In this method, the step of stacking a prepreg containing a glass cloth and a copper foil are repeated multiple times. Thus, foreign matters may be incorporated in each step.
Recently, to solve these problems, a material free from a glass cloth in which an insulating resin layer is directly stacked on a copper foil known as Resin Coated Copper (RCC) has been used for manufacturing a multilayer printed circuit board. It allows for manufacturing a thin multilayer printed wiring board, so that demand for RCC has been significantly increased (see, for example, Patent Reference 1).
However, when such a material free from a base material such as a glass cloth is stacked by a conventional pressurizing procedure, the resin may flow out during stacking under heating and pressure. Therefore, it is difficult to precisely control a thickness of an insulating resin layer. Furthermore, the material is so thin that it cannot be easily handled and defects such as break and bending of the material may lead to a low yield and thus to a high cost. In addition, when another component is mounted on a printed circuit board prepared by stacking such an insulating resin layer, rigidity of the printed circuit board cannot be maintained due to the absence of a base material such as a glass cloth, so that warpage may occur in the printed circuit board, leading to defective connection between the component and the printed circuit board.
Patent Reference 1: Japanese Published Unexamined Application No. 2000-244114.